Hidden within the seemingly endless list of strange biological partnerships, the tale of two microbial life forms who enjoy dining together is one the most fascinating.
Deep down in the continental margins or our oceans, low temperatures and high pressure force methane inside what are essentially ice crystals called methane hydrates. These crystals are important for two reasons: their potential as an energy source, and their potential as a global warming contributor.
With steadily rising ocean temperatures, along with the ever-present risk for earthquakes, both of which could both force the methane into our oceans (and atmosphere), these crystals have become a particularly pressing concern for climate scientists.
But, to understand the positive and negative implications of these deepwater crystals in a warming world, we must glean information from those who feast upon the energy-rich sources of methane.
Amongst these hydrates, there lives two microbes, one a Bacteria and one an Archaea. In phylogenetic terms, it is the cooperation between these bacteria and archaea (a sulfite-utilizing deltaproteobacteria and an anaerobic methanotrophic archaea, respectively) that scientists are observing. While each are from different domains of life, they work together to create “beautiful bundles” that eat methane and convert it into both a source of carbon and a source of energy for the microbes.
A new study published in the journal, Environmental Microbiology, has attempted to look at this process by observing the teammates and then parsing how they go about eating the methane they seem to like so much. Sponsored by the Department of Energy, the NASA Astrobiology Institute and the National Science Foundation, this was a major study with important backers.
“We want to understand on a gene level and on a chemical level, what’s going on in these processes, and then understand how this is going to change in the future with global warming and rising CO2,” Glass said.
For an up-close view of this unique co-op on the ocean floor, the team used the underwater submersible robot Jason, an unmanned, remotely operated vehicle (ROV) that can stay underwater for days at a time.
What the researchers found was that a rare earth metal, Tungsten – also used as filaments in light bulbs – was found in the partner microbes.
“This is the first evidence for a microbial tungsten enzyme in low temperature ecosystems,” said Jennifer Glass, an assistant professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology.
Taking samples of sediment, the researches sequenced the genes and proteins of these, and discovered that an enzyme used by microbes to “eat” methane may need tungsten to operate. The enzyme (formylmethanofuran dehydrogenase) is the final stop in the pathway of converting methane to carbon dioxide, an essential step for methane oxidation.
Micro-organisms in low-temp environments typically use molybdenum, which offers similar chemical properties to tungsten but is usually much more widely available (tungsten is directly below molybdenum on the periodic table).
Why these archaea appear to use tungsten is unknown. One guess is that tungsten may come in a form that makes it easier for organisms to use in methane seeps, but questions such as these must be answered in follow-up studies.
Until then, they are certainly off to a great start in learning more about the breakdown of methane, a particularly strong greenhouse gas, which could have huge implications in our fight against man-made global warming, and the preservation of our oceans.
